Influence of Peroxisomal Import and Receptor Recycling of Peroxisomal Function
Ratzel, Sarah E.
Doctor of Philosophy
Peroxisomes compartmentalize a variety of important metabolic reactions including fatty acid β-oxidation and the related process of IBA β-oxidation. Peroxisomal proteins are encoded by nuclear genes and must be post-translationally imported. A dynamic import process is vital for proper matrix protein localization and is dependent on the family of peroxin (PEX) proteins. The delivery and peroxisomal import of cargo from a loaded receptor, PEX5 or PEX7, is carried out by the early-acting peroxins, including PEX13 and PEX14, and receptor recycling is carried out by the late-acting peroxins, including PEX4 and PEX6. In this thesis, I describe the use of double mutant analysis to differentiate early-acting and late-acting pex mutants by phenotypic and molecular analysis. I found that double mutants made with two early-acting or two late-acting pex mutants showed enhanced phenotypes in β-oxidation and import defects. In contrast, defects of double mutants made with a weak early-acting mutant and a late-acting mutant were suppressed. Additionally, I found that receptor localization is central to proper peroxisomal function. My results suggest that when the receptor is not removed from the peroxisome, stabilized peroxisomal pores may be formed, perhaps impairing peroxisomal function due to leaching of peroxisomal contents. Together my data suggest that balance between import and receptor recycling is fundamental for peroxisomal function. In humans, peroxisomal biogenesis disorders are most often caused by defects in late-acting peroxins. Peroxisomal defects occur in plants and humans as a result of the same lesions in PEX proteins. The understanding of how these late-acting defects can be ameliorated in plants, may inspire new approaches to human therapeutics.